Because it was said :
18.20 Ezekiel - The one who sins is the one who will die. The child will not share the guilt of the parent, nor will the parent share the guilt of the child.
So we don't share the guilt of Adam and Eve.
There are two kinds of sin mentioned in the Bible....1) the sin (imperfection, defects) inherited from Adam....and 2) the sins we commit as a wilfull and deliberate action, despite knowing that it is wrong.
What you mention is the second kind. No one can be held accountable for the deliberate sin of a parent, or child....but no one can dodge inherited sin. Only Jesus' sacrifice could pay to redeem humanity from slavery to sin and death, restoring God's original purpose for the human race....to "fill the earth and subdue it" as God intended at the beginning. They were to transform the whole earth into an Edenic paradise and enjoy everlasting life in peace and security under God's loving rulership. This will yet be realised. (Isaiah 55:11)
I don't remember everything as I read quite a long time ago the Bible, but I remember few things like :
4.1 - Levitic The Lord said to Moses, 2 “Say to the Israelites: ‘When anyone sins unintentionally and does what is forbidden in any of the Lord’s commands—
And then it explains what to do.
Also I think that the jews have probably others way to ask forgiveness maybe just by prayers. I don't know but I'm not sure they still sacrifice animals each time they sin. In our times it's complicated.
Yes, under God's law given through Moses, God made arrangements to allow the sacrifice of animals to atone for sin. Blood represents life, so this arrangement was to stay in force until Messiah came to give his precious blood, once for all time.
And why you believe in the original sin if it wasn't teached by the other prophets before ?
This means there was already a way to ask for forgiveness and that what the people who lived before Jesus used to do.
Why believing more in Paul than the prophets ? That's what I don't understand.
As I understand it, original sin, was atoned for by Jesus. Animal sacrifices were temporary and had to be offered regularly for sins committed against the law of God. Once Jesus offered the ultimate sacrifice, there was no longer a need to offer animals. Their blood pointed forward to the one act of atonement that would remove the need for animals to be offered (as an apology for sin)....forever.
Paul, in no way contradicted anything in OT scripture, nor did he teach anything that was in opposition to Christ's teachings.
Perhaps you misunderstand because Christendom had messed up the Bible's message. I had to abandon Christendom to find the truth.....just as the Jews had messed up their worship in the first century, and some who had become "lost" were led out of that corrupted system, so in these last days, Jesus has again led his disciples out of a corrupted religious system.
That is what I believe.